There is some kind of black fluffy/spongy insulation (?) behind the ceiling registers (between the plastic register and the ceiling, around the hole). I noticed a couple of registers had these material dirty/moldy. I am trying to replace them. I asked the company that cleaned the air ducts in my house. They don't know. I checked at Home Depot without any luck.
Can anybody tell me where I can buy this? Looks like I can easily install them myself if I know where to get it.